1. Field of the Invention
The present invention relates to an apparatus for measuring a specific molecule included in a specimen and in particular to an optical biosensor.
2. Description of the Related Art
A planar lightwave circuit sensor using optical waveguide phenomenon is widely spread as the sensor to measure the amount of the bio molecules existing in body fluid such as blood. As shown in FIG. 1, the planar lightwave circuit has a light source 6 , a substrate 1 receiving a light from the light source 6, a first grating 3 delineated on the substrate 1 so as to receive an incident light, a second grating 4 delineated on the substrate 1 so as to diffract the incident light in the direction of the exterior, and the photo detector 7 receiving the diffracted light. Further, the planar lightwave circuit sensor has a single optical waveguide membrane 2 disposed on the substrate 1 so as to transmit the incident light, and a glucose oxidase (GOD) membrane 5 disposed on the optical waveguide membrane 2. The GOD membrane 5 identifies the bio molecules and transforms the information about the amount of the identified bio molecules to a change of an optical intensity.
An existing method for analyzing the bio molecules existing in the blood by the planar lightwave circuit sensor is as follows. At first, the blood is collected from vein with a syringe. The collected blood is dropped on the GOD membrane 5. The laser light is emitted from the light source 6 and diffracted by the first grating 3. The diffracted light penetrates the optical waveguide membrane 2. The evanescent wave is generated at the interface between the optical waveguide membrane 2 and the GOD membrane 5. The intensity of the evanescent wave changes by reaction between the dropped bio molecules contained in the blood and the GOD. The photo detector 7 receives the diffracted light from the second grating 4 and detects the changes of the evanescent wave intensity to analyze the bio molecules contained in the blood as disclosed in Japanese Patent Application Hei9-61346.
However, manufacturing the evanescent wave generates requires precision apparatus and techniques. This is because the incident light reaching at the interface should be diffracted at appropriate angle to measure the change of the evanescent wave intensity precisely.